From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 15 Aug 2019 18:14:16 +0200
Subject: [PATCH 1/4] cgroup: Remove ->css_rstat_flush()
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: da77ceac3d20f27310a07a7c346a4ee6b40d6c28
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

I was looking at the lifetime of the the ->css_rstat_flush() to see if
cgroup_rstat_cpu_lock should remain a raw_spinlock_t. I didn't find any
users and is unused since it was introduced in commit
  8f53470bab042 ("cgroup: Add cgroup_subsys->css_rstat_flush()")

Remove the css_rstat_flush callback because it has no users.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
---
 include/linux/cgroup-defs.h |    5 -----
 kernel/cgroup/cgroup.c      |   12 ------------
 kernel/cgroup/rstat.c       |   10 +---------
 blk-cgroup.c                |    1 -
 4 files changed, 1 insertion(+), 27 deletions(-)

--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -144,9 +144,6 @@ struct cgroup_subsys_state {
 	struct list_head sibling;
 	struct list_head children;
 
-	/* flush target list anchored at cgrp->rstat_css_list */
-	struct list_head rstat_css_node;
-
 	/*
 	 * PI: Subsys-unique ID.  0 is unused and root is always 1.  The
 	 * matching css can be looked up using css_from_id().
@@ -455,7 +452,6 @@ struct cgroup {
 
 	/* per-cpu recursive resource statistics */
 	struct cgroup_rstat_cpu __percpu *rstat_cpu;
-	struct list_head rstat_css_list;
 
 	/* cgroup basic resource statistics */
 	struct cgroup_base_stat pending_bstat;	/* pending from children */
@@ -633,7 +629,6 @@ struct cgroup_subsys {
 	void (*css_released)(struct cgroup_subsys_state *css);
 	void (*css_free)(struct cgroup_subsys_state *css);
 	void (*css_reset)(struct cgroup_subsys_state *css);
-	void (*css_rstat_flush)(struct cgroup_subsys_state *css, int cpu);
 	int (*css_extra_stat_show)(struct seq_file *seq,
 				   struct cgroup_subsys_state *css);
 
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1957,7 +1957,6 @@ static void init_cgroup_housekeeping(str
 	cgrp->dom_cgrp = cgrp;
 	cgrp->max_descendants = INT_MAX;
 	cgrp->max_depth = INT_MAX;
-	INIT_LIST_HEAD(&cgrp->rstat_css_list);
 	prev_cputime_init(&cgrp->prev_cputime);
 
 	for_each_subsys(ss, ssid)
@@ -5013,12 +5012,6 @@ static void css_release_work_fn(struct w
 	list_del_rcu(&css->sibling);
 
 	if (ss) {
-		/* css release path */
-		if (!list_empty(&css->rstat_css_node)) {
-			cgroup_rstat_flush(cgrp);
-			list_del_rcu(&css->rstat_css_node);
-		}
-
 		cgroup_idr_replace(&ss->css_idr, NULL, css->id);
 		if (ss->css_released)
 			ss->css_released(css);
@@ -5080,7 +5073,6 @@ static void init_and_link_css(struct cgr
 	css->id = -1;
 	INIT_LIST_HEAD(&css->sibling);
 	INIT_LIST_HEAD(&css->children);
-	INIT_LIST_HEAD(&css->rstat_css_node);
 	css->serial_nr = css_serial_nr_next++;
 	atomic_set(&css->online_cnt, 0);
 
@@ -5089,9 +5081,6 @@ static void init_and_link_css(struct cgr
 		css_get(css->parent);
 	}
 
-	if (cgroup_on_dfl(cgrp) && ss->css_rstat_flush)
-		list_add_rcu(&css->rstat_css_node, &cgrp->rstat_css_list);
-
 	BUG_ON(cgroup_css(cgrp, ss));
 }
 
@@ -5193,7 +5182,6 @@ static struct cgroup_subsys_state *css_c
 err_list_del:
 	list_del_rcu(&css->sibling);
 err_free_css:
-	list_del_rcu(&css->rstat_css_node);
 	INIT_RCU_WORK(&css->destroy_rwork, css_free_rwork_fn);
 	queue_rcu_work(cgroup_destroy_wq, &css->destroy_rwork);
 	return ERR_PTR(err);
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -162,17 +162,9 @@ static void cgroup_rstat_flush_locked(st
 		struct cgroup *pos = NULL;
 
 		raw_spin_lock(cpu_lock);
-		while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
-			struct cgroup_subsys_state *css;
-
+		while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu)))
 			cgroup_base_stat_flush(pos, cpu);
 
-			rcu_read_lock();
-			list_for_each_entry_rcu(css, &pos->rstat_css_list,
-						rstat_css_node)
-				css->ss->css_rstat_flush(css, cpu);
-			rcu_read_unlock();
-		}
 		raw_spin_unlock(cpu_lock);
 
 		/* if @may_sleep, play nice and yield if necessary */
--- a/block/blk-cgroup.c	2020-09-14 16:06:15.279320628 +0100
+++ b/block/blk-cgroup.c	2020-09-14 16:09:05.975267928 +0100
@@ -1258,7 +1258,6 @@
 	.css_offline = blkcg_css_offline,
 	.css_free = blkcg_css_free,
 	.can_attach = blkcg_can_attach,
-	.css_rstat_flush = blkcg_rstat_flush,
 	.bind = blkcg_bind,
 	.dfl_cftypes = blkcg_files,
 	.legacy_cftypes = blkcg_legacy_files,